A durable bioprosthetic vascular graft is badly needed for vascular bypass surgery. For peripheral vascular surgery, there is essentially no viable alternative to an autogenous venous conduit to bypass leg arteries. In part, the challenges to establishing an endothelialized graft have been gaps in our understanding of how specific growth factors and matrix proteins interact with each other and modulate cellular responses. Heparins are known to modulate growth responses, but heparin's effects have been confusing and contradictory, due to the heterogeneity of heparin's structure and its diverse interactions. We have discovered that vascular endothelial growth factor (VEGF) and fibronectin (Fn) have a unique and dedicated biologic partnership. Fn binds VEGF like no other matrix protein, and Fn significantly enhances the endothelial migration and proliferation mediated by VEGF. Their cognate receptors, alpha5beta1 and VEGFR2 also work in synergy. We have also demonstrated that VEGF-Fn complexes uniquely enhance the differentiation of endothelial progenitor cells (EPC) into the endothelial line. Our goals are: 1) Elucidate the mechanisms underlying Fn promotion of VEGF activity, 2) Define the structure-activity relations of heparin's modulation of VEGF-VEGFR2 binding, 3) Define and develop recombinant fibronectin constructs and heparin oligosaccharides that when combined with VEGF and EPC will enhance endothelialization of a porous vascular graft, by capillary in growth and the differentiation of EPC. Using recombinant Fn constructs, we will identify the Fn domains that are key to promoting VEGF mitogenic effects. Using structurally defined synthetic oligosaccharides, and novel surface plasmon resonance technology we will identify the optimal size and structure of heparin that promotes VEGF binding to its receptor VEGFR2. In an animal model of peripheral artery bypass grafting that closely resembles the human condition, we will test these constructs and cells for their ability to promote the growth of a stable endothelial lining.